Design And Application Of Carbon-Based Bimetallic Oxygen Electrode For Rechargeable Zn-Air Batteries

Rechargeable zinc-air batteries,a low-cost and eco-friendly technique,have shown their promises to be the next-generation energy storage and conversion devices.However,the large-scale application of zinc-air batteries is limited by the slow kinetics of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）during the catalytic conversion of oxygen on the cathode.Optimized bifunctional electrocatalysts are often required to reduce the activation energy barrier.While platinum group metal（PGM）based catalysts have excellent ORR or OER catalytic activity,their large-scale commercial applications are hindered by high cost and scarcity.Benefiting from the merits of large specific surface area,good physicochemical stability and tunable properties with changing structure/morphology,Metal-based carbon materials have attracted wide attention.While the catalytic performance of single metal based carbon materials is limited,the synergistic effect of the two metals can confer higher catalytic performance on carbon materials.In this paper,carbon-based bimetallic oxygen electrocatalyst is regard as the research goal.According to the difference of electronic structure and electronegativity between different metals,the electronic structure of Fe is regulated to improve the bi-functional catalytic activity of carbon-based composite materials.Therefore,it is critically important for successful commercialization of large scale zinc-air batteries.The contents are as follows:（1）As is know,the metal aggregation will lead to the insufficient number of active sites.On the basis of molten salt template and source of N and S,porous carbon-based catalysts embedded with Fe Co nanoclusters(Fe Co_/1:2/PNSC)has been synthesized as air cathode for rechargebale zinc-air batteries.More importantly,due to the high electronegativity of Co,it could compete for the external electrons of Fe nanoclusters,activating the electronic state of Fe.This enhanced the binding of Fe and N and promoted the intermediates adsorption around Fe atoms.The optimal Fe Co_/1:2/PNSC sample exhibited the excellent bifunctional oxygen catalytic activities in alkaline electrolyte.The constructed Fe Co_/1:2/PNSC-based zinc-air cell displayed high power density(138m Wcm^-2).（2）In order to further promote the combination of Fe and N atoms,Fe₂N nanoparticles were composited with nitrogen-doped carbon foam via CeO₂ engineering as bi-functional oxygen electrocatalyst for rechargeable zinc-air batteries.The structural characterization and performance tests revealed that the excitation of oxygen vacancies in CeO₂ accelerated the migration of oxygen species and enhanced the oxygen storage/release capacity of the as-prepared catalyst.Meanwhile,the oxygen vacancy of CeO₂ enabled the timely discharge of gas bubbles from the reaction system.In addition,a large number of pyridine-N species were induced by CeO₂-doping and sequentially anchored in the carbon matrix.As a result,the Fe₂N active state was formed through the strengthened binding of Fe-N atoms and thus improved the ORR activity.The optimal CeO₂-Fe₂N/NFC_-2 catalyst sample showed a good OER performance(E_j=10=266 m V)and ORR electrocatalytic activity(E_1/2=0.87 V).The Zn-air battery assembled by CeO₂-Fe₂N/NFC_-2 catalyst could deliver 6500 cycles at the current density of 20 m A cm^-2,achieving long-term stability of rechargeable zinc-air battery.（3）For promoting the catalytic activity of carbon-based iron materials and the external electronic environment of Fe atoms,VN and Fe heterojunction inserted N-doped carbon foamed was synthesized and used as air cathode for rechargebale zinc-air batteries.The results showed that there was strong interfacial electron interaction between VN as a solid ligand and ultrafine Fe nanoclusters.The characteristic high price state and low electronegativity of V element promoted the electron transfer from V to Fe atom,which enhanced the electron cloud density of Fe and thus promoted electron transfer during the reaction.The optimized Fe-VN_（1:1）/NFC material showed highly efficient ORR performance(E_1/2=0.87 V)and OER electrocatalytic activity(E_j=10=246m V).The Zn-air battery displayed a high power density(146 m W cm^-2)and specific capacity(779 m Ah g^-1).